1. Field of the Invention
The packaging of light-emitting diode (LED) basically has two types. One is LAMP type, which uses liquid resin for encapsulation. The present invention mainly uses the packaging process for SMD LED and also includes the new packaging technology of LED Chip on Board (COB).
2. Description of the Prior Art
The consideration of heat dissipation in LED package is very important, especially in the newest lighting application of white light LED, which no longer uses 15 mA or 20 mA as standard, but above 50 mA, even up to 100 mA (more brightness). Therefore, its power consumption is large, and heat generated is large as well. Hence, the heat dissipation ability should be enhanced. Hewlett Packard has developed a type of LED (called Super Flux LEDs by HP in model number HPWA-MHOO etc.) with special packaging structure (commonly called Perona fish), designed for good heat dissipation and can withstand up to 70 MA current (20 MA for traditional package). At present, LED of this type is mostly used in the third braking lights of automobiles.
In terms of heat dissipation in LED package, current surface mount device (SMD) is one of the worst, even worse than Lamp LED. Large current can not be sustained. The main reason for this is that effective heat conductance can not be achieved due to the poor heat dissipation of packaging resin and substrate itself.
Besides, traditional SMD LED mostly does not have reflective bases. There are few companies to include reflective base design in their products. The existing SMD LED with a reflective base mostly has recess on the printed circuit boards (substrates). The metal reflective layers are applied by plating, followed by die bonding, wire bonding and encapsulation before finished SMD LED products are made, as described in a Taiwan Patent with Publication No.381313. Because the bottom inside the concave cup reflecting base made on printed circuit board through drilling holes is in curved shape (cause by drilling holes), the connection for die bonding of LED chips is poor and unstable. Normal concave cup bottom should be flat to facilitate die bonding. Therefore, the technology has the above shortcoming and poor heat conductance.
For the first embodiment of the LED package in the present invention, it is first to directly drill holes (not digging holes) at the positions that need placement of LED chips, followed by through-hole plating (a general printed circuit board process), followed by passing printed circuit board through solder furnace to completely fill all through-hole plated holes with high-temperature solder, followed by pressing solder points with molds to form a groove, which is for die bonding of LED chips and reflection, followed by gold or silver plating on groove surface to form highly reflective metal films, finally followed by die bonding, wire bonding and encapsulation.
The greatest feature of the present invention is to use printed circuit board (PCB) process technology to fill up the through-hole position with high-temperature solder (above 250xc2x0 C.), followed by bonding a groove reflector at that position with the use of the solder point for heat conductance and connection with heat dissipating material at bottom. Therefore, the present technology can directly use LED Chip On Board to make LED for traffic signal lights that have better performance than traditional products of Lamp type, lower process and material cost and superior heat dissipating ability. The technology can also be used for other LED lighting product development.
The main purpose of using high-temperature solder furnace (above 250xc2x0 C.) in the first embodiment is to prevent the appearance of the high temperature up to 120xc2x0 C. caused by heat generated from LED chips subject to long-term high current (above 30 mA). If common types of solder (183xc2x0 C., Sn63%, Pb37%) is used, solder softening or solder crystal growth or low-temperature alloy will appear.
To avoid these things from happening and causing quality problems with LED reliability, the present invention specially emphasizes the use of high-temperature solder at about 250xc2x0 C.-500xc2x0 C., most preferably 350xc2x0 C. Of course, most soldering material is composed of Sn/Pb alloys. If the groove surface is plated with highly reflective materials like Ag or Au, the performance of groove reflector will be affected because Sn easily forms alloys with Au and Ag. Therefore, in the present invention an isolating layer of Cr or other layers that are not easy to form low-temperature alloys with solder material is plated prior to plating gold or silver film. Thus, the adverse effect can be avoided when the SMD LED connected with other printed circuit board in the present technology passes through the solder furnace and are subject to high temperature.
The inventor has been dedicated to LED research for many years, obtaining several patents and making excellent achievement. In view of the problem with poor heat dissipation associated with SMD LED and LED Chip On Board, the inventor has spent tremendous efforts in finding the solution and new manufacturing process that mass production is feasible and has good competitive strength and production value.